Removing dynamically added controls from WinForm

Question

I have a GroupBox in which I dynamically add controls into it. The controls I add are of two types DevExpress.XtraEditors.TextEdit and Windows.Forms.Label I am trying to remove these controls using the following

foreach (Control control in salesBox.Controls)
{
  control.Dispose(); 
  salesBox.Controls.Remove(control);
} 

This is correctly removing the TextEdit controls but not the Label controls. The loop is not iterating through the Label controls.

Answer 1

It doesn't work because you are modifying the collection you are iterating. Calling the Dispose() method also removes a control from the parent's Control collection. The side-effect is that you'll only dispose the even numbered controls. Either of these two loops will get the job done:

while (salesBox.Controls.Count > 0) salesBox.Controls[0].Dispose();

for (int ix = salesBox.Controls.Count-1; ix >= 0; ix---) salesBox.Controls[ix].Dispose();

Or keep them on a panel and dispose the panel.

Answer 2

The easiest way to remove all controls from a controls collection is to call its Clear method:

salesBox.Controls.Clear();

---

Modifying collections can invalidate enumerators and yield unpredictable results or even throw an InvalidOperationException , depending on the collection type (see the "Remarks" section in IEnumerable.GetEnumerator Method on MSDN). Since foreach uses an enumerator you should not alter the collection it is iterating.

Use a for statement, if you have to delete selectively and also iterate backwards, in order not to get wrong index values after removing items:

for (int i = salesBox.Controls.Count - 1; i >= 0; i--) {
    Control c = salesBox.Controls[i];
    if (c is TextEdit || c is Label) {
        salesBox.Controls.RemoveAt(i);
    }
}

Answer 3

You cannot alter the contents of the collection within the Foreach. You would need to do something like this I believe.

List<Control> toRemove = salesBox.Controls.OfType<Control>().ToList();

foreach(Control c in toRemove)
{
 salesBox.Controls.Remove(c);
 c.Dispose();
}

Answer 4

Foreach can't iterate because the length of the salesbox.Controls changed. If you add or remove an item you'd better use for You can do it by

   for(int i=0;i<salesBox.Controls.Count;i++)
    {      if(salesBox.Controls[i] is DevExpress.XtraEditors.TextEdit) //your condition here
           { 
             salesBox.Controls.Remove(salesBox.Controls[i]);
             i--;
          }
    }